Robert Pershing Wadlow was a man who lived in the first half of the twentieth century. He had hyperplasia of his pituitary gland, which caused him over-produce human growth hormone (HGH), and as a result, he grew to nearly 9 feet (2.75m). He had difficulty managing his body size and died at age 22, with no sign that this growth was slowing down.
HGH can be used for medicinal purposes, and it seems that doctors prescribe it for conditions like chronic underdevelopment and HGH deficiencies.
Putting aside ethical or government regulation issues, is it theoretically possible for someone (like a "fully grown" adult) to artificially grow beyond their genetic potential by providing them with regular doses of HGH? If not, what was different about Wadlow's case?